The "bio-duck" noise is a mysterious sound that submarine operators and scientists have been hearing in Antarctic waters since the 1960s. Nobody was sure what generated the repeated, quack-like pulsing sound — until now.

In a paper to be released tomorrow in Biology Letters, marine biologist Denise Risch and her team identify the sound as belonging to the minke whale, which they overheard emitting the noise while it was diving for food.

Very little is known about these whales' vocalizations; researchers have identified only a few of the various minke species' sounds, including a "boing" and what's called a "Star Wars" vocalization. In 2013, researchers for the first time placed acoustic tags on the Antarctic minke (Balaenoptera bonaerensis). Tags from two whales recorded some sounds already linked to the species.

But over the course of 18 hours, one of the tags picked up bio-duck beats before and during a whale's feeding dive. Because researchers following the whales saw no other marine mammals nearby, Risch and colleagues conclude April 23 in Biology Letters that minke whales are the bio-ducks.

You can also hear the scientists who made this discovery talking about it (and playing more of the sounds) on a NOAA podcast.